4 Barrel Rochester Quadrajet

what is the cfm of a stock 1977 4 Barrel Rochester Quadrajet?

i think all quads are like 750cfm except the one that came on the 500 caddy which is 800

Thanks for that link Jerry......

Most Q-jets where 750cfm. 800's came on:

455's, 500's, and Stage cars.

The Q-jet seems to have a unique way of letting the engine use just what it needs, even though the carb has a fairly large CFM capacity. The small primaries may have a lot to do with that, but I don't understand that much about them. I believe it's a great carb for the street/daily driver.
I had a new Pontiac Tempest Sprint in 1966, with the OHC six in it, and it had a Q-jet on it, with only 230 cubic inches in the engine, so the carb is really quite interesting in the way it deals with a wide range in engine sizes.

The throttle plate opens primary and secondary plates manually just like a double pumper. The flaps at the top of the carburetor over the secondaries (otherwise known as an air valve) are what regulate the air flow through the secondaries.

The air valve is regulated with a spring that can be adjusted while its on the car. If this adjustment is too loose and lets the valve open too quickly, it bogs down- hence the slang name of Quadra-bog because they didn't understand how it worked. If it is too tight, you wont get max air flow.

The beauty of this carb is that if your engine only needs 600 cfm, the air valve will only open up enough to flow 600 cfm.

YUP

I looked on the Sean Murphy site yesterday. I think his carbs are reasonable in price, for whatever they were built for, like stage 1, 2, etc.

Most Q-jets from 1974 and earlier (4mV or 4MC) are 750CFM Most of the car Q-jets 1975 and later (the M4MC's and M4ME's)(trucks used the earlier 4MV style till 1979) were either 800 or 850 CFM. There are exceptions, particularly some of the performance BOP Q-jets. You can usually tell by looking down the primary bores and if you see a little "bump", its one of the higher CFM units.

memory serves me right they are a variable 750 cfm

bigredlaguna wrote:
The beauty of this carb is that if your engine only needs 600 cfm, the air valve will only open up enough to flow 600 cfm.

Kinda reminds me of the old predator carbs from back in the day, variable venturi was a great idea, but they had a hard time selling the technology to the "set in their ways" old timer racers

ooooo, I think I may have one of these lurking about in a junk drawer somewhere, I may have to give it a try again.